Page 116 - Introduction to Petroleum Engineering

102 PETROLEUM GEOLOGY

Crust Mantle

Outer core

Inner
core

Crust–mantle boundary
(Moho)

FIGURE 6.1 The interior of the Earth.

Continental crust
(granitic) Oceanic crust
Sea level (basaltic)

Crust
Moho

Mantle
Asthenosphere

FIGURE 6.2 The lithosphere.

A relatively thin crust is above the mantle. Figure 6.2 is a sketch of the crust of the
Earth. The granitic continental crust is composed principally of silica and aluminum;
the oceanic crust contains silica and magnesia. Underlying the continental and
oceanic crusts is a layer of basalt. The boundary between the crustal basalt and the
semimolten basalt of the mantle is the Mohorovicic discontinuity, or Moho for short.
The combination of crust and solid basalt above the Moho is known as the lithosphere.
The upper mantle below the Moho that behaves elastically is part of the lithosphere. The
asthenosphere is below the lithosphere and contains the part of the upper mantle that
is ductile. The lithosphere and asthenosphere are separated by the lithosphere–
asthenosphere boundary (LAB).